Biomolecules play key roles in regulating the precipitation of CaCO 3 biominerals but their response to ocean acidification is poorly understood. We analysed the skeletal intracrystalline amino acids of massive, tropical Porites spp. corals cultured over different seawater pCO 2. We find that concentrations of total amino acids, aspartic acid/asparagine (Asx), glutamic acid/glutamine and alanine are positively correlated with seawater pCO 2 and inversely correlated with seawater pH. Almost all variance in calcification rates between corals can be explained by changes in the skeletal total amino acid, Asx, serine and alanine concentrations combined with the calcification media pH (a likely indicator of the dissolved inorganic carbon available to support calcification). We show that aspartic acid inhibits aragonite precipitation from seawater in vitro, at the pH, saturation state and approximate aspartic acid concentrations inferred to occur at the coral calcification site. Reducing seawater saturation state and increasing [aspartic acid], as occurs in some corals at high pCO 2 , both serve to increase the degree of inhibition, indicating that biomolecules may contribute to reduced coral calcification rates under ocean acidification.
Resolving how factors such as temperature, pH, biomolecules and mineral growth rate influence the geochemistry and structure of biogenic CaCO3, is essential to the effective development of palaeoproxies. Here we optimise a method to precipitate the CaCO3 polymorph aragonite from seawater, under tightly controlled conditions that simulate the saturation state (Ω) of coral calcification fluids. We then use the method to explore the influence of aspartic acid (one of the most abundant amino acids in coral skeletons) on aragonite structure and morphology. Using ≥200 mg of aragonite seed (surface area 0.84 m2), to provide a surface for mineral growth, in a 330 mL seawater volume, generates reproducible estimates of precipitation rate over Ωaragonite = 6.9–19.2. However, unseeded precipitations are highly variable in duration and do not provide consistent estimates of precipitation rate. Low concentrations of aspartic acid (1–10 μM) promote aragonite formation, but high concentrations (≥ 1 mM) inhibit precipitation. The Raman spectra of aragonite precipitated in vitro can be separated from the signature of the starting seed by ensuring that at least 60% of the analysed aragonite is precipitated in vitro (equivalent to using a seed of 200 mg and precipitating 300 mg aragonite in vitro). Aspartic acid concentrations ≥ 1mM caused a significant increase in the full width half maxima of the Raman aragonite v1 peak, reflective of increased rotational disorder in the aragonite structure. Changes in the organic content of coral skeletons can drive variations in the FWHM of the Raman aragonite ν1 peak, and if not accounted for, may confuse the interpretation of calcification fluid saturation state from this parameter.
<p>There is strong evidence that the source of terrestrial carbon and iron geochemistry play an important role in organic carbon transport and preservation in coastal and marine sediments <sup>1,2,3</sup>. There is a global drive to increase forestry and Scotland is undergoing a period of afforestation<sup>4</sup>. A portion of this is being planted in sea loch (fjord) catchments; however the effect of this increase in forestry on coastal carbon transport and storage is poorly understood. Fjord systems have recently been identified as significant terrestrial carbon stores<sup>5</sup> therefore understanding how afforestation of these catchments changes the carbon dynamics from source to sea, is key.</p><p>In this study Mossbauer spectroscopy, XRD and XRF are used to examine how iron concentration and speciation differs within Scottish fjord sediments. This preliminary data provides insight of the variation in iron speciation in fjord systems, processes controlling iron transport and speciation and potential mineral binding mechanisms in coastal sediments. This enables us to start addressing key knowledge gaps in the transport of organic carbon and iron from land (forested source areas) to sea (fjords). Thus, contributing to our overarching aim of tracing the movement and interactions of organic carbon across the terrestrial - aquatic interface.</p><p>Through this project, further analytical techniques such as biomarker analysis, isotopic analysis and SEM, will be used to improve our understanding of source to sea processes in fjord systems throughout the northern hemisphere. This will hopefully enable improved understanding and quantification of local and national carbon stocks. Further insights into carbon and iron burial mechanisms may allow us to tailor land use and management around fjord environments to maximise natural carbon storage.</p>
<p>Mid-latitude fjords have recently been identified as important environments for carbon storage. This research highlights the importance of the lateral transport of carbon from land to sea as we assess the influence of catchment land use (primarily forestry) on carbon transport and sediment carbon burial. Establishing the influence of land use, specifically forestry, on coastal biogeochemical cycling is particularly important if afforestation is to help mitigate climate change impacts, and to better understand the impact of deforestation. The relationship between carbon and iron in fjord sediments is the focus of this study. We provide insights into carbon and iron coupling in a mid-latitude fjord. Here we show the variability of carbon burial, and how this is influenced by terrestrial inputs and iron speciation in fjord sediments. We use bulk organic carbon and elemental data, isotopic analysis, M&#246;ssbauer spectroscopy and chemical extractions to better understand the relationship between carbon and iron. Observed decreases in organic carbon from the upper to lower basin are influenced by the input of terrestrial material. Organic carbon is up to three times higher in the upper basin and terrestrial organic carbon is ~20% higher in comparison to the lower basin of the fjord. The strength of the reactive iron signal is found to vary vertically (with depth, over time) and laterally (from upper &#8211; lower basin) within this fjord. Results highlight that there is a changing relationship between iron and carbon within this system. Understanding land-sea controls on coastal carbon transport and burial is crucial during this period of climate change.</p>
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